This invention relates to pump dispensers, particularly for viscous products such as toothpaste and the like, and more especially relates to a positive discharge valve for the dispenser.
U.S Pat. No. 4,629,097 discloses a viscous product pump dispenser having a discharge spout in communication with a hollow piston stem which therewith defines an unvalved discharge passage.
When filling the dispenser product is loaded to fill the discharge passage as much as possible. Thus the loaded dispenser may be shipped fully primed. Otherwise, if the discharge passage is partially filled, it becomes necessary to assist the priming action by pressing inwardly on the lower piston follower normally provided for such dispensers.
However, a filled discharge passage, even partially, presents a number of problems. During storge, the product in the spout can dry out or lose its flavor. Otherwise, product could unintentionally ooze from the spout if the dispenser is dropped or exposed to adverse ambient conditions. Still further, voids or bubbles in the product could affect pump priming during use.
Another pump dispenser for viscous products is disclosed in U.S. Pat. No. 4,511,068 having a one-way flap valve located in the discharge passage such that downward movement of the piston causes the exerted pressure to be transmitted to the viscous product contained within the container to thereby open the valve. Similar problems are encountered as in the aforedescribed valveless discharge dispenser in that upon filling the dispenser under pressure the product could easily open the flap valve and enter the spout where it is exposed to air and could become dried or caked or could ooze out of the spout or be inadvertently extruded if the dispenser is dropped in any attitude. Messy conditions are therefore encountered with the use of these dispensers.